Last Updated: Jan 19, 2022
Back in elementary and middle school, most of us probably learned about phase changes. If this still isn't ringing a bell, think about how H20 (water, that is), can change from one state to another without changing its chemical composition. The ice cubes in your tea, the water vapor causing mold to grow in your home, and the stuff that comes out of our shower heads are all the same thing, chemically speaking. However, the process of changing from a solid to a liquid or gas requires energy. In recent years, sustainable building companies have been exploring pathways that would allow builders to harness and store this natural release of energy to increase the energy performance of homes.
The main problem is that most of the materials at our disposal for constructing our homes have melting and freezing points that are much too extreme for human comfort. Some people enjoy sleeping underneath a warm blanket, but using the phase change of water to ice would mean that we would be stuck with interior home temperatures of 32 degrees Fahrenheit. Different synthetic and natural materials, however, have melting and freezing points that are close to comfortable room temperature.
Phase change building materials are still mostly in the development phase. However, in this short article, we offer an introduction to how phase change building materials might be able to help create more energy-efficient, comfortable homes.
Most sustainable construction methodologies today focus on high-performance insulation and a tight building envelope. Combining these two building strategies, alongside passive solar heating design, can drastically reduce the need for mechanical cooling and heating systems. Heating and air conditioning account for about 48 percent of all residential energy usage. Finding ways to reduce reliance on HVAC systems is one of the central goals of low-carbon homes.
However, before the day and age of high-performance foam insulation and energy-efficient heat pumps, homeowners used other strategies to keep their houses warm without having to cut down an entire forest for firewood. Thermal mass refers to the given properties of the mass of a home, which enables it to store heat, providing "inertia" against temperature fluctuations.
Heavy, dense building materials were once common in constructing the walls and floors of homes, including brick, block, stone, and adobe. These materials' sheer weight and mass allowed the house to "suck up" the heat from the sun and radiate that heat back into the home during cooler evenings and nights.
Today, many builders, unfortunately, focus on lightweight, quick construction methods, focusing on 2x4s and plywood. These building methods do cost less. However, most builders choose not to incorporate thermal mass into their homes because of the added material and labor costs. For this reason, the vast majority of homes in America today have virtually no thermal mass to help naturally regulate indoor temperatures.
Specific phase change materials, such as plasterboards (which we will review below), offer the opportunity to enjoy the benefits of thermal mass without the added weight (and labor cost) that this building strategy would entail in today's housing market.
As we mentioned in the introduction, phase change materials are elements that can change from solid to liquid and liquid to solid. For home construction purposes, certain substances with carefully selected melting points are used to store and release heat to affect and control the temperature within a home.
Without getting too scientific, the necessary process behind how phase change materials work goes as follows:
Many people don't realize that phase change materials will not change during the process of change. The most commonly cited example is that when ice is melting, the temperature will stay steady at 32 degrees Fahrenheit while ice is still present. The possible use of phase change materials for homes hinges on the opportunity to store that generated but latent heat for release later.
As we have stated above, whenever a material melts or solidifies, it will absorb or release energy. Materials that will melt or solidify at room temperatures can potentially contribute to the regulation of home temperature. The most common phase change materials studied for sustainable home products are paraffin waxes and certain fatty acids.
In essence, a paraffin wax that melts at 73 degrees Fahrenheit could offer similar benefits to thermal mass. During warm afternoons, this wax could melt, and the latent energy from that warming process could be stored for release during cooler evenings. With modern-day technology, the main benefit is that Nano-particles of paraffin wax could be incorporated into lightweight building materials such as plywood or drywall.
Phase change materials could offer the same benefits as massive adobe, brick, or rock walls without the cost and added weight these traditional vernacular construction methods entail.
Phase change materials present an exciting opportunity for sustainable building strategies and methodologies. The release of energy during melting or solidification is an entirely natural form of energy. It could potentially replace a part of our reliance on fossil fuel sources of energy for our homes. Unfortunately, most phase change building materials are still being studied in laboratories and universities around the world.
One exciting and inspiring application is the Knauf Comfortboard, a type of interior plasterboard or drywall that incorporates a synthetic, paraffin wax-based phase change material. Advertised as "thermal mass without the weight," this interior plasterboard includes Micronal, which is an acrylic phase change material designed to provide thermal regulation to improve comfort and climate conditions.
The Micronal inside the plasterboard can absorb heat energy during the day and releases it at night. This allows for a steadier interior temperature without having to rely on artificial heating and cooling. This plasterboard, which is available in certain countries of Europe and South America, can be installed just like regular gypsum plasterboard, making for easy incorporation in renovations.
While phase change materials still require more research and development, they offer an exciting opportunity and frontier for sustainable homes.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.